Mechanism for Guaranteeing Delivery of Multi-Packet GSM Message

ABSTRACT

A target task ensures complete delivery of a global shared memory (GSM) message from an originating task to the target task. The target task&#39;s HFI receives a first of multiple GSM packets generated from a single GSM message sent from the originating task. The HFI logic assigns a sequence number and corresponding tuple to track receipt of the complete GSM message. The sequence number is unique relative to other sequence numbers assigned to GSM messages that have not been completely received from the initiating task. The HFI updates a count value within the tuple, which comprises the sequence number and the count value for the first GSM packet and for each subsequent GSM packet received for the GSM message. The HFI determines when receipt of the GSM message is complete by comparing the count value with a count total retrieved from the packet header.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to the following co-pending U.S.patent applications, filed on even date herewith and incorporated hereinby reference in their entirety:

-   -   Attorney Docket No.: AUS920070330US1, entitled “Method, System        and Program Product for Reserving a Global Address Space;    -   Attorney Docket No.: AUS920070331US1, entitled “Method, System        and Program Product for Allocating a Global Shared Memory;”    -   Attorney Docket No.: AUS920070332US1, entitled “Notification to        Task of Completion of GSM Operations By Initiator Node;”    -   Attorney Docket No.: AUS920070333US1, entitled “Issuing Global        Shared Memory Operations Via Direct Cache Injection to a Host        Fabric Interface;”    -   Attorney Docket No.: AUS920070334US1, entitled “Mechanisms to        Order Global Shared Memory Operations;”    -   Attorney Docket No.: AUS920070335US1, entitled “Host Fabric        Interface (HFI) to Perform Global Shared Memory (GSM)        Operations;”    -   Attorney Docket No.: AUS920070336US1, entitled “Mechanism to        Prevent Illegal Access to Task Address Space by Unauthorized        Tasks;”    -   Attorney Docket No.: AUS920070337US1, entitled “Mechanism to        Perform Debugging of Global Shared Memory (GSM) Operations;”    -   Attorney Docket No.: AUS920070338US1, entitled “Mechanism to        Provide Reliability Through Packet Drop Detection;”    -   Attorney Docket No.: AUS920070339US1, entitled “Mechanism to        Provide Software Guaranteed Reliability for GSM Operations;”    -   Attorney Docket No.: AUS920071056US1, entitled “Notification By        Task of Completion of GSM Operations at Target Node;”    -   Attorney Docket No.: AUS920071057US1, entitled “Generating and        issuing Global Shared Memory Operations Via a Send FIFO;”

GOVERNMENT RIGHTS

This invention was made with United States Government support underAgreement No. HR0011-07-9-0002 awarded by DARPA. The Government hascertain rights in the invention.

BACKGROUND

1. Technical Field

The present invention generally relates to data processing systems andin particular to distributed data processing systems. Still moreparticularly, the present invention relates to data processing systemsconfigured to support execution of global shared memory (GSM)operations.

2. Description of the Related Art

It is well-known in the computer arts that greater computer systemperformance can be achieved by harnessing the processing power ofmultiple individual processing units. Multi-processor (MP) computersystems can be designed with a number of different topologies, of whichvarious ones may be better suited for particular applications dependingupon the performance requirements and software environment of eachapplication. One common MP computer architecture is a symmetricmulti-processor (SMP) architecture in which multiple processing units,each supported by a multi-level cache hierarchy, share a common pool ofresources, such as a system memory and input/output (I/O) subsystem,which are often coupled to a shared system interconnect.

Although SMP computer systems permit the use of relatively simpleinter-processor communication and data sharing methodologies, SMPcomputer systems have limited scalability. For example, many SMParchitectures suffer to a certain extent from bandwidth limitations,especially at the system memory, as the system scale increases.

An alternative MP computer system topology known as non-uniform memoryaccess (NUMA) has also been employed to addresses limitations to thescalability and expandability of SMP computer systems. A conventionalNUMA computer system includes a switch or other global interconnect towhich multiple nodes, which can each be implemented as a small-scale SMPsystem, are connected. Processing units in the nodes enjoy relativelylow access latencies for data contained in the local system memory ofthe processing units' respective nodes, but suffer significantly higheraccess latencies for data contained in the system memories in remotenodes. Thus, access latencies to system memory are non-uniform. Becauseeach node has its own resources, NUMA systems have potentially higherscalability than SMP systems.

Regardless of whether an SMP, NUMA or other MP data processing systemarchitecture is employed, it is typical that each processing unitaccesses data residing in memory-mapped storage locations (whether inphysical system memory, cache memory or another system resource) byutilizing real addresses to identifying the storage locations ofinterest. An important characteristic of real addresses is that there isa unique real address for each memory-mapped physical storage location.

Because the one-to-one correspondence between memory-mapped physicalstorage locations and real addresses necessarily limits the number ofstorage locations that can be referenced by software, the processingunits of most commercial MP data processing systems employ memoryvirtualization to enlarge the number of addressable locations. In fact,the size of the virtual memory address space can be orders of magnitudegreater than the size of the real address space. Thus, in a conventionalsystems, processing units internally reference memory locations by thevirtual (or effective) addresses and then perform virtual-to-realaddress translations (often via one or more intermediate logical addressspaces) to access the physical memory locations identified by the realaddresses.

Given the availability of the above MP systems, one further developmentin data processing technology has been the introduction of parallelcomputing. With parallel computing, multiple processor nodes areinterconnected to each other via a system interconnect or fabric. Thesemultiple processor nodes are then utilized to execute specific tasks,which may be individual/independent tasks or parts of a large job thatis made up of multiple tasks. In these conventional MP systems withseparate nodes connected to each other, there is no convenient supportfor tasks associated with a single job to share parts of their addressspace across physical or logical partitions or nodes.

Shared application processing among different devices provides a veryrudimentary solution to parallel processing. However, with each of thesesystems, each node operates independently of each other and requiresaccess to the entire amount of resources (virtual address space mappedto the local physical memory) for processing any one job, making itdifficult to productively scale parallel computing to a large number ofnodes.

SUMMARY OF ILLUSTRATIVE EMBODIMENTS

Disclosed are a method, processing node, and computer program productfor ensuring complete delivery of a global shared memory (GSM) messagefrom an originating task on a first node coupled to a network fabric ofa distributed network via a HFI to a target task on a second node alsocoupled to the network fabric via a host fabric interface (HFI). The HFIreceives a first GSM packet of a plurality of GSM packets generated froma single GSM message being sent from the originating task. The HFI logicassigns a sequence number to track receipt of the GSM message from theoriginating task. The sequence number is unique relative to othersequence numbers assigned to GSM messages from the same originating taskthat have not been completely received. The HFI then updates a countvalue within a tuple comprising the sequence number and the count valuefor the first GSM packet. The HFI continues to update the count valuefor each subsequent GSM packet received for the GSM message. The HFIdetermines when receipt of the GSM message is complete by comparing thecount value with a count total retrieved from the packet header.

In one embodiment, when all the GSM packets of a GSM message have beenreceived, the HFI generates and issues a notification of completion tothe target task. The HFI also clears (zeros) out the count value of thecorresponding tuple, so that the tuple (or sequence number) can beutilized to track receipt of GSM packages for a next GSM message.

The above as well as additional objectives, features, and advantages ofthe present invention will become apparent in the following detailedwritten description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself, as well as a preferred mode of use, furtherobjects, and advantages thereof, will best be understood by reference tothe following detailed description of an illustrative embodiment whenread in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates an example multi-node data processing system with ahost fabric interface (HFI) provided at each node to enable GSMprocessing across the nodes, according to one embodiment of theinvention;

FIG. 2 illustrates the allocation of tasks of a single job acrosspartitions and nodes within a multi-node GSM environment (such as dataprocessing system of FIG. 1), according to one embodiment of theinvention;

FIGS. 3A and 3B illustrates two example allocations of global addressspace (GAS) among multiple tasks of a job to enable GSM operations,according to alternate embodiments of the invention;

FIG. 4 is a block diagram illustrating components of an example send(initiating) node and target node utilized for processing of GSMoperations, according to one embodiment of the invention;

FIG. 5 illustrates a detailed view of an example HFI window and theassociation of window entries to specific memory locations within thereal (i.e., physical) memory, in accordance with one embodiment of theinvention;

FIG. 6 is a flow chart of the method of initiating/establishing a jobwithin the GSM environment, including allocating tasks to specific nodesand assigning windows within the HFI, in accordance with one embodimentof the invention;

FIG. 7 is a flow chart illustrating the method by which the HFIprocesses a command generated by a task executing on the local node, inaccordance with one embodiment of the invention;

FIG. 8 is a flow chart illustrating the method by which the HFIgenerates and transmits a GSM packet, in accordance with one embodimentof the invention;

FIG. 9 is a flow chart of the method by which incoming GSM packets areprocessed by the HFI and the HFI window of a target/receiving node,according to one embodiment of the invention;

FIG. 10 is a block diagram representation of entries within an exampleGSM command and GSM packet, in accordance with one embodiment of theinvention;

FIG. 11 is a flow chart illustrating the method by which the HFIgenerates a GSM packet, in accordance with one embodiment of theinvention; and

FIG. 12 is a flow chart illustrating the method by which the targetnode's HFI and target task provide guaranteed delivery via sequencenumber and count tuples, in accordance with one embodiment of theinvention.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

The illustrative embodiments provide a method and data processing systemfor generating and processing global shared memory (GSM) operations thatcomplete parallel job execution of multiple tasks on different physicalnodes with distributed physical memory that is accessible via a single,shared, global address space (GAS). Each physical node of the dataprocessing system has a host fabric interface (HFI), which includes oneor more HFI windows with each window assigned to at most onelocally-executing task of the parallel job, although multiple windowsmay be assigned to a single task. The HFI includes processing logic forcompleting a plurality of operations that enable parallel job executionvia the different tasks, each of which maps only a portion of theeffective addresses (EAs) of the shared GAS to the local (real orphysical) memory of that node. Each executing task within a node isassigned a window within the local HFI. The window ensures that issuedGSM operations (of the local task) are correctly tagged with the job IDas well as the correct target node and window identification at whichthe operation is supported (i.e., the EA is memory mapped). The windowalso enables received GSM operations with valid EAs in the task to whichthe window is assigned to be processed when received from another taskexecuting at another physical node, while preventing processing ofreceived operations that do not provide a valid EA to local memorymapping.

In the following detailed description of exemplary embodiments of theinvention, specific exemplary embodiments in which the invention may bepracticed are described in sufficient detail to enable those skilled inthe art to practice the invention, and it is to be understood that otherembodiments may be utilized and that logical, architectural,programmatic, mechanical, electrical and other changes may be madewithout departing from the spirit or scope of the present invention. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims.

Within the descriptions of the figures, similar elements are providedsimilar names and reference numerals as those of the previous figure(s).Where a later figure utilizes the element in a different context or withdifferent functionality, the element is provided a different leadingnumeral representative of the figure number (e.g, 1xx for FIGS. 1 and2xx for FIG. 2). The specific numerals assigned to the elements areprovided solely to aid in the description and not meant to imply anylimitations (structural or functional) on the invention.

It is understood that the use of specific component, device and/orparameter names are for example only and not meant to imply anylimitations on the invention. The invention may thus be implemented withdifferent nomenclature/terminology utilized to describe thecomponents/devices/parameters herein, without limitation. Each termutilized herein is to be given its broadest interpretation given thecontext in which that terms is utilized. Specifically, the followingterms, which are utilized herein, are defined as follows:

-   -   (1) Effective, virtual, and real address spaces: a user-level        program uses effective addresses (EAs), which are translated        into operating system (OS)-specific virtual addresses (VAs). The        OS and the hardware memory management units (MMUs) translate VAs        into real addresses (RAs) at the time of use.    -   (2) Node: the set of computing resources that form the domain of        a coherent operating system (OS) image.    -   (3) Cluster: a collection of two or more nodes.    -   (4) System: the collection of all nodes in the cluster domain.    -   (5) Parallel Job: an application that executes on some or all        the nodes in a cluster. A job is made up of tasks (processes),        each of which executes in a node domain in the cluster. A        parallel job has various attributes including a job ID that        uniquely identifies the parallel tasks that comprise the        parallel job in the entire system.    -   (6) Task: a single process that executes within a single        effective address (EA) space. By definition, a task executes        wholly within a node. However, multiple tasks in a parallel job        may execute on the same node (typically proportional to the        number of CPUs on the node). A task can include one or more        threads of control that all view and share the same effective        address (EA) space.    -   (7) Global shared memory (GSM)-enabled job: a parallel job, in        which the component tasks have arranged to make parts of their        individual effective address (EA) spaces accessible to each        other via global shared memory (GSM) operations.    -   (8) Global address space (GAS): the union of all effective        addresses (EAs) in a GSM job that are accessible to more than        one task via GSM operations.    -   (9) Global address: an effective address within a task described        as <T, EA> that is accessible to other tasks.    -   (10) Home: the specific node where a particular location in the        global address space (GAS) is physically allocated in physical        memory. Every location in the GAS has exactly one home.

As further described below, implementation of the functional features ofthe invention is provided within computing nodes and involves use of acombination of hardware and several software-level constructs. Thepresented figures illustrate both hardware and software componentswithin an example GSM environment in which two physically separatenodes, interconnected via respective HFIs and an interconnect, provide adata processing system that executes a parallel job as individual tasksthat utilize a GSM. The presentation herein of only two nodes, i.e., aninitiating (sending) node and a target (receiving) node, is providedsolely to simplify the description of the functionalities associatedwith GSM operations and the HFI. It is appreciated that this GSMfunctionality enables scaling to a much larger number of processingnodes within a single data processing system.

With specific reference now to the figures, and in particular to FIG.1A, there is illustrated a high-level block diagram depicting a firstview of an exemplary data processing system 100 configured with twonodes connected via respective host fabric interfaces, according to oneillustrative embodiment of the invention, and within which many of thefunctional features of the invention may be implemented. As shown, dataprocessing system 100 includes multiple processing nodes 102A, 102B(collectively 102) for processing data and instructions. Processingnodes 102 are coupled via host fabric interface (HFI) 120 to aninterconnect fabric 110 that supports data communication betweenprocessing nodes 102 in accordance with one or more interconnect and/ornetwork protocols. Interconnect fabric 110 may be implemented, forexample, utilizing one or more buses, switches and/or networks. Any oneof multiple mechanisms may be utilized by the HFI 120 to communicateacross the interconnect 110. For example, and without limitation, HFI120 may communicate via a proprietary protocol or an industry standardprotocol such as Inifiniband, Ethernet, or IP (Internet Protocol).

As utilized herein, the term “processing node” (or simply node) isdefined as the set of computing resources that form the domain of acoherent operating system (OS) image. For clarity, it should beunderstood that, depending on configuration, a single physical systemmay include multiple nodes. The number of processing nodes 102 deployedin a given system is implementation-dependent and can vary widely, forexample, from a few nodes to many thousand nodes.

Each processing node 102 may be implemented, for example, as a singleintegrated circuit chip (e.g., system-on-a-chip (SOC)), a multi-chipmodule (MCM), or circuit board, which contains one or more processingunits 104 (e.g., processing units 104A, 104B) for processinginstructions and data. Further, each processing unit 104 mayconcurrently execute one or more hardware threads of execution.

As shown, each processing unit 104 is supported by cache memory 112,which contains one or more levels of in-line or lookaside cache. As isknown in the art, cache memories 112 provide processing units 104 withlow latency access to instructions and data received from source(s)within the same processing node 102 a and/or remote processing node(s)102 b. The processing units 104 within each processing node 102 arecoupled to a local interconnect 114, which may be implemented, forexample, with one or more buses and/or switches. Local interconnect 114is further coupled to HFI 120 to support data communication betweenprocessing nodes 102A, 102B.

As further illustrated in FIG. 1A, processing nodes 102 typicallyinclude at least one memory controller 106, which may be coupled tolocal interconnect 114 to provide an interface to a respective physicalsystem memory 108. In alternative embodiments of the invention, one ormore memory controllers 106 can be coupled to interconnect fabric 110 ordirectly to a processing unit 104 rather than a local interconnect 114.

In addition to memory controller, each processing unit 104 also includesa memory management unit (MMU) 105 to translate effective addresses toreal (or physical) addresses. These MMUs 105 perform EA-to-RAtranslations for tasks executing on processing nodes (e.g., node 102A)of data processing system 100. However, the invention also uses aseparate MMU 121, which is coupled to the local interconnect 114. MMU121 performs EA-to-RA translations for operations received from tasksoperating on remote processing nodes (e.g., node 102B) of dataprocessing system 100. In one implementation of processorconfigurations, MMU 121 may be integrated with HFI 120 so as to supportEA-to-RA address translations required by HFI and/or tasks utilizing HFIto complete GSM operations.

The HFI 120A and functional components thereof, which are describedbelow, enables the task(s) executing on processing units 104 a/104 b togenerate operations to access the physical memory 108B of other nodesthat are executing other tasks of the parallel job using EAs from ashared global address space (GAS) and a GSM. Likewise, HFI 120B enablesaccess by the task(s) on initiating node 102A to access physical memory108B when certain criteria are met. These criteria are described belowwith reference to FIGS. 4 and 9

Those skilled in the art will appreciate that data processing system 100of FIGS. 1A and 1B can include many additional components, which are notillustrated herein, such as interconnect bridges, non-volatile storage,ports for connection to networks or attached devices, etc. Because suchadditional components are not necessary for an understanding of thepresent invention, they are not illustrated in FIG. 1A or 1B ordiscussed further herein.

The above described physical representations of nodes of an example dataprocessing systems 100 with HFIs supports the distribution of tasksassociated with a parallel job across multiple nodes within a largersystem with a GSM. FIG. 2 illustrates a high level view of processingmultiple tasks of a parallel job within an exemplary softwareenvironment for data processing system 100, in accordance with oneembodiment. In the exemplary embodiment, data processing system 100includes at least two physical systems 200 a and 200 b (whichrespectively provide processing nodes 102 a and 102 b of FIG. 1) coupledby interconnect fabric 110. In the depicted embodiment, each physicalsystem 200 includes at least two concurrent nodes. That is, physicalsystem 200 a includes a first node corresponding to operating system 204a 1 and a second node corresponding to operating system 204 a 2.Similarly, physical system 200 a includes a first node corresponding tooperating system 204 b 1 and a second node corresponding to operatingsystem 204 b 2. The operating systems 204 concurrently executing withineach physical system 200 may be homogeneous or heterogeneous. Notably,for simplicity, only one node of each physical system is utilized in thedescriptions of the GSM and HFI functions herein, although the featuresof the invention are fully applicable to tasks executing on any one ofmultiple nodes on a single physical system accessing physical memory ofother nodes on other physical system(s).

Each physical system 200 may further include an instance of a hypervisor202 (also referred to as a Virtual Machine Monitor (VMM)). Hypervisor202 is a program that manages the full virtualization orpara-virtualization of the resources of physical system 200 and servesas an operating system supervisor. As such, hypervisor 202 governs thecreation and destruction of nodes and the allocation of the resources ofthe physical system 200 between nodes.

In accordance with the present invention, the execution of parallel jobsin data processing system 100 is facilitated by the implementation of anew shared memory paradigm referred to herein as global shared memory(GSM), which enables multiple nodes executing tasks of a parallel job toaccess a shared effective address space, referred to herein as a globaladdress space (GAS).

Thus, under the GSM model employed by the present invention, dataprocessing system 100 can execute multiple different types of tasks.First, data processing system 100 can execute conventional (individual)Tasks C, F, G, K, L, P, Q, T, V and W, which are independently executedunder operating systems 204. Second, data processing system 100 canexecute parallel jobs, such as Job 2, with tasks that are confined to asingle node. That is, Tasks D and E are executed within the nodecorresponding to operating system 204 a 1 of physical system 200 a andcan coherently share memory. Third, data processing system 100 canexecute parallel jobs, such as Job 1, that span multiple nodes and evenmultiple physical systems 200. For example, in the depicted operatingscenario, Tasks A and B of Job 1 execute on operating system 204 a 1,Tasks H and J of Job 1 execute on operating system 204 a 2, Tasks M andN of Job 1 execute on operating system 204 b 1, and Tasks R and S of Job1 execute on operating system 204 b 2. As is illustrated, tasks ofmultiple different jobs (e.g., Job 1 and Job 2) are permitted toconcurrently execute within a single node.

With standard task-to-task operation, tasks running on a same node,i.e., tasks homed on the same physical device, do not need to utilizethe HFI and resolve EA-to-RA mapping beyond the standard page table. TheHFI and/or MMU components are thus not utilized when exchangingoperations across tasks on the same physical node. Where tasks arerunning on different physical nodes, however, the use of the MMU and HFIis required to enable correct EA-to-RA translations for tasks homed atthe specific node when issuing and/or receiving GSM operations.

Additional applications can optionally be executed under operatingsystems 204 to facilitate the creation and execution of jobs. Forexample, FIG. 2 depicts a job management program 206, such asLoadLeveler, executing under operating system 204 a 1 and a runtimeenvironment 208, such as Parallel Operating Environment (POE), executingunder operating system 204 a 2. LoadLeveler (206) and Parallel OperatingEnvironment (208) are both commercially available products availablefrom International Business Machines (IBM) Corporation of Armonk, N.Y.LoadLeveler (206) and POE (208) can be utilized as a convenience to theuser, but are not required. However, the described embodiment providesfor the availability of a privileged program to both bootstrapnon-privileged executables on the cluster nodes and to enable thenon-privileged executables to request and use node resources.

In the following descriptions, headings or section labels are providedto separate functional descriptions of portions of the inventionprovided in specific sections. These headings are provided to enablebetter flow in the presentation of the illustrative embodiments, and arenot meant to imply any limitation on the invention or with respect toany of the general functions described within a particular section.Material presented in any one section may be applicable to a nextsection and vice versa.

A. Task Generation and Global Distribution

The method for generating and distributing the tasks of a job (e.g., Job1, illustrated in FIG. 2), are described in FIG. 6. The executable ofthe program is supplied to the job management program 206, withuser-supplied execution attributes in a job command file. Theseattributes include the number of nodes on which the job needs toexecute. The job management program 206 generates a job ID (that isunique system-wide) and selects a set of nodes in the system on which toexecute the parallel job. The job management program 206 then invokesthe runtime system 208 for parallel jobs (e.g., (POE)). The runtimesystem 208 in turn spawns the user executable on the set of nodes thatthe job management program 206 allocated for the parallel job, and theruntime system 208 sets up state that permits each task to determine thetask's unique rank ordering within the parallel job. For example, in ajob with N tasks, exactly one task will have the rank order i, where0<=i<N. The runtime system 208 also provides the mapping (in the form ofa table) between the tasks and the physical nodes on which the tasks areexecuting. Setup operations performed by the job management program 206also permit the tasks to access interconnect resources on each clusternode.

In order to complete the processing by the HFI and other functionalfeatures of the invention, a system-level establishment (or systemallocation) of the global shared memory is required. FIGS. 3A-3Billustrate two embodiments of assigning tasks to address spaces withinthe global address space during setup/establishment of the GSMenvironment. The complete description of this process is presentedwithin co-pending patent applications, Ser. Nos. ______ and/or ______(Atty. Doc. No. AUS920070330US1/AUS920070331US1). Relevant content ofthose applications are incorporated herein by reference.

During initialization of the tasks of a parallel job, each task issues asystem call to set up the global address space. In addition to reservingeffective address space, the system call also accomplishes twoadditional tasks. First, the call initializes a HFI window hardwarestructure in preparation for usage in the global shared memory model.Second, the system call creates a send FIFO and a receive FIFO, whichallow the task to send active messages to one another via the node'sHFI.

Once the global address space has been initialized, individual tasks canallocate physical memory that can be globally addressed by all tasks ofthe job. Memory allocation on each task is achieved through a secondsystem call, which specifies the amount of memory to be allocated, aswell as the effective address within the already-reserved global addressspace (GAS) where the allocated memory must appear. All allocations aredone locally with respect to the task issuing the second system call.Once allocation is completed, all threads within the locally-executedtask can access the allocated memory using load and store instructions.

In order to use the GSM feature, each of the group of tasks for the jobhas to communicate the results of the first system call and co-ordinateamongst each other the arguments to the second system call invocation.FIG. 6, described below, illustrates the method by which theseinter-task coordination of system calls are completed.

Referring now to FIG. 3A, there is depicted a representation of anexemplary effective address space of tasks of a parallel job followingthe establishment of the GAS. In the exemplary embodiment, parallel job300 comprising ten tasks, labeled Task 0 though Task 9. Each of the tentasks is allocated a respective one of effective address (EA) spaces302A-302 i by its operating system 204. These effective address spacesare allocated to each task independent of the existence of the othertasks. After each task issues an initialization system call, a portionof the effective address (EA) space on that task is reserved for useexclusively for performing global shared memory (GSM) allocations, asillustrated at reference numerals 304A-304 i.

With reference now to FIG. 3B, there is illustrated a representation ofan exemplary effective address space of tasks comprising a parallel jobfollowing the allocation of memory in the GAS 304A-304 i. In thedepicted example, the allocation for a shared array X[ ] distributedacross the GAS 304A-304 i is shown. In particular, region 306A isallocated to X[0]-X[9] in GAS 304A of Task 0, region 306B is allocatedto X[10]-X[19] in GAS 304B of Task 1, and so on until finallyX[90]-X[99] is allocated in region 306 i of GAS 304 i. The portions ofX[ ] allocated to the GAS 304 of a task are homed on the node executingthat task. Physical memory 308A-308 i is further allocated on eachtask's node to back the portion of X[ ] homed on that node.

FIGS. 3A and 3B provide two alternative methods though which the arrayx[ ] can be allocated. For instance, as shown in FIG. 3A, array x[ ] canbe allocated such that the array can be accessed with contiguouseffective addresses within the global address space of all ten (10)tasks participating in the parallel job. The global address space canalso be caused to begin at the same effective address on each task,through the co-ordination of arguments to the second system callinvocation. FIG. 6, described later, illustrates the method by whichthese inter-task coordination of system calls are completed. Sharedarray x[ ] can also be allocated in a non-contiguous manner within theglobal address space. Finally, the global address space can start atdifferent effective addresses within the tasks.

For the allocations in FIGS. 3A and 3B, the operating system of the nodeon which each task executes only allocates backing memory for thoseportions of the task global address space that are homed on that node.Elements 308 a through 308 i in each figure show how the physical memorymay be allocated to store the portion of the array x[ ] homed at thatnode. As shown, for tasks 0, 1, and 9, the allocation in FIG. 3A takesseven physical pages while that in FIG. 3B takes six physical pages.Every access to a shared variable in a GSM application must betranslated into a tuple of the form <T, EA>, where EA is the effectiveaddress on task T where the location is homed.

Practicality in data structure placement is a very importantconsideration since practicality can have a huge impact on the amount ofphysical memory required to support the allocation. For instance, if theprogrammer specifies that the shared array x should be distributed in acyclic manner, an extensive amount of fragmentation and wasted physicalmemory will result if the array were to be allocated such that the arraycan be contiguously addressed within the global address space. For suchan allocation, savings in the amount of physical memory required to backup the homed portions of x[ ] would be achieved by compacting the datastructure. The GSM feature described herein thus provides applicationswith considerable flexibility in deciding how to map global datastructures. As FIGS. 3A 3B show, simplicity in determining where ashared element is homed can be traded off against the fragmentationcosts of the chosen mapping scheme.

Using the above allocation of GAS to tasks of a job, the embodiments ofthe invention enables a job to be scaled across a large number of nodesand permits applications to globally share as large a portion of theapplication's effective address space as permitted by the operatingsystem on each node. Also, no restrictions are imposed on where thetasks of a job must execute, and tasks belonging to multiple jobs areallowed to execute concurrently on the same node.

B. HFI, HFI Windows Send and Receive FIFO, MMU and Memory Mapping

Referring now to FIG. 4, there is illustrated another more detailed viewof the data processing system 100 of FIGS. 1 and 2 with the hardware(and software) constructs required for generation, transmission, receiptand processing of GSM operations across physical nodes within the GSMenvironment. First computer node 102 a (initiating or sending node) andsecond computer node 102 b (target or receiving node) includes HFI 120a, 120 b, respectively. HFI 120 is a hardware construct that sits on thecoherent fabric within a (processor) chip. Each HFI 120 provides one ormore windows 445 (and 446) (see FIG. 5) allocated to a particularexecuting task of a parallel job.

When an executing task of a parallel job issues an initialization systemcall, the operating system (OS) of that node attempts to establish adedicated window on the HFI for that task. If the operation succeeds, aportion of the allocated HFI window is first mapped into the task'saddress space. The memory mapped IO (MMIO) space 460 includes a commandarea and FIFO pointers. After the appropriate portion of the task'seffective address space is reserved (i.e., mapped to the physicalmemory), the operating system sets up the window to point to the pagetable for that task so that effective addresses within inbound (i.e.,from the interconnect 410) GSM commands can be translated.

In processing system 100, first node 102 a represents thesending/initiating node and is illustrated with send FIFO 407 withinmemory 405 that is accessible via a MMIO 460. Second node 102 brepresents the receiving or target node and is illustrated with receiveFIFO 408 within its memory 406. It is understood that even though anasymmetric view is shown, both processing nodes 102 a and 102 b aresimilarly configured, having both send FIFO 407 and receive FIFO 408,and each node is capable of performing both send and receive functions.Within processing system, 100, the HFI 110 is the primary hardwareelement that manages access to the interconnect (410). The interconnectis generally represented by links 455 a, 455 b routing switch 410, and aseries of switch elements 450A, 450B and 460. HFI 120A thus enables atask executing on sending node (120 a) to send GSM operations (with adestination or target identified by the job ID, node ID and window ID)to a receiving/target node 102 b.

As further illustrated in FIG. 4, processing nodes 102 include at leastone memory controller 106, which is coupled to local fabric 414 toprovide an interface between HFI 120 and respective physical systemmemory (DIMMs) 408. Processing nodes 102 also include MMU 121, which iscoupled to fabric bus 414. MMU 121 may be a part of (i.e., integratedinto) HFI 120 and provides the EA-to-RA translation required for GSMoperation processing by the HFI 120. Coupled to fabric bus 414 isprocessor cache 412, which is in turn connected to processing units ofthe central processor. Also illustrated is (form the perspective of theexecuting task), a view of the mapping of EAs to physical memory space405 allocated to the executing task. Within this virtual view of thephysical memory is a send FIFO 407 which is used to store commands anddata generated by the task, prior to being processed by HFI 120 togenerate GSM operations. Also illustrated is HFI doorbell 409, which isa mechanism that tracks the number of operations within send FIFO, andis utilized to alert the HFI 120 when to retrieve operations from thesend FIFO 407. Similarly, receive FIFO 408 of target node 102 b islocated within physical memory 406, in which an EA mapping location 404is also identified for reference.

The HFI window 445 and 446 provide a task-level view into the node'shardware that enables GSM commands to be launched with regards to aparticular task's effective address space (302) and for the effectiveaddresses (EA) contained within commands to be appropriately translated.HFI windows 445 are basic system constructs used for GSM operations.Each HFI 120 may contain multiple windows 445, and each window isallocated to a single task of the one or more tasks executing on thecomputer node 102.

Further functional characteristics of example HFI windows 445 areillustrated by FIG. 5, which is now described. As shown by FIG. 5, HFI120 consists of a plurality of windows (window0 through windowN) ofwhich HFI window2 445 is selected as the example window. Each HFI has afixed number of windows, each of which can belong to exactly one task,although more than one window may be assigned to a task. The windowassigned to a task is used by the HFI 120 to both launch GSM messagesoriginating from the task as well as handle incoming messages accessingthat task's effective address space. HFI window 445 is accessible bytask-generated commands, which may be generated at different functionallevels, including by a user 550, an OS 552, and/or a hypervisor 554.

HFI window 445 consists of a plurality of functional entries, such ascommand entries, credentials entry, an address translation entry, anddata structures used by the HFI to control message transmission andreception. Specifically, as illustrated, window2 445 comprises thefollowing entries, without limitation, HFI command count 510, send FIFOEA 514, SEND RDMA FIFO EA 515, receive FIFO EA 516, epoch vector EA 518,credentials 512, and fence counters 520. In the illustrative embodiment,credentials 512 includes the job ID (also referred to herein as a jobkey), process ID, LPAR (logical partition) ID and EA key. The HFIreferences the credentials 512 to correctly authenticate an incoming GSMtransaction as being authorized to perform an operation on theassociated task's effective address space. It is appreciated that thedifferent components of credentials 512 may also be represented with itsown entry within HFI window 445. Each of the above entries are registersproviding a value of a memory location at which the named entry isstored or at which the named entry begins (i.e., a start location)within the effective address space of the task. These effectiveaddresses are translated by MMU 121 into corresponding real addressesthat are homed within the physical memory 530. HFI forwards one of theeffective addresses of Window contents to MMU 121, and MMU 121translates the effective address into a real address corresponding tothe physical memory 530 to which the EAs of the task identified by thecredentials are mapped.

HFI window 445 also comprises one or more fence counters 520 fortracking completion of GSM operations during a local fence operation anda global fence operation. The fence counters 520 referenced by the EAsin map to fence counter 540 within the real memory location assigned tothe task. In order to assist with local (task-issued) fence operations,the RA space assigned to the task also includes a send-op counter 542 totrack the completion of task-issued commands, which are initially storedin send FIFO 532, before passing to HFI window for processing.

Thus, as further illustrated, send FIFO EA 514 holds the start effectiveaddress for the task's send FIFO, which address can be translated by MMU121 to point to the start (real address) of send FIFO 532 in physicalmemory 530. Likewise, receive FIFO EA 516 holds the start EA of thetask's receive FIFO 534, which address is translated by MMU 121, andpoints to the start address in physical memory 530 of the receive FIFO534 of the task. The SEND RDMA FIFO EA 515 and epoch vector EA 518similarly can be translated by MMU 121 to point to the start realaddresses of the SEND RDMA FIFO 536 and Epoch vector 538, respectively.Note that while the send FIFO 514 and receive FIFO 516 may be contiguousin the effective address space of the task to which that windowcorresponds, these FIFOs (514, 516) may be discontiguous in real(physical) memory 530.

Each HFI window contains key resources including the pointer to theaddress translation tables that are used to resolve the effectiveaddress (with respect to a particular task) into a real address. Thewindow number within the HFI that is allocated for the GSMinitialization operation is returned back to the user as an opaquehandle, which may contain an encoding (embedding) of the node and windownumber, along with the effective address where the global address spaceis reserved within that task's effective address space. The languagerun-time takes on the responsibility for communicating each task'swindow identity to all other tasks that wish to issue GSM commands tothat task. If a task has multiple threads of control, atomicity to theHFI window has to be ensured either through normal intra-task lockingprimitives, or by assigning each thread its own distinct HFI window.Finally, HFI performance counters for all traffic based on that windoware also mapped into the task's address space. This permits the task toeasily monitor statistics on the interconnect traffic.

HFI windows may be shared amongst one or more logical partitions. If asingle node is partitioned, the operating system running on a partitionmay only have access to a subset of the total number of supportedwindows. The OS may further reserve a subset of these windows for kernelsubsystems such as the IP device driver. The remaining windows may beavailable for use by the tasks executing within that partition.

When a window is allocated on the HFI, the operating system tags thewindow with the identity of the job to which the task belongs. Duringissuance of GSM operations, all outgoing packets are automaticallytagged by the HFI with the job id. Outgoing packets also specify aparticular window on the destination/target node's HFI 120B in whosecontext the GSM effective address must be translated. The HFI comparesthe job ID contained within the GSM packet against the job id containedwithin the window. If the job ID's do not match, the packet is silentlydiscarded. Statistics that count such packets can be used to gentlydissuade system users from either unintentionally or maliciouslyflooding the system with such packets.

Thus, unauthorized access to a task's effective address space is notpermitted during the course of global shared memory operations. A taskis able to send a GSM operation to any task belonging to any job runninganywhere in the entire system. However, the HFI will perform the GSMoperations on the targeted task's effective address space if and only ifan incoming GSM command belongs to the same job as the task whoseaddress space the command manipulates. A further granulation of job IDsis also possible, whereby a task can give specific authorization to onlya subset of the tasks executing within the job. This can be done by asubset of the tasks requesting a different job ID to be associated tothem, causing that job ID to be installed into the HFI window associatedwith these tasks.

In order to fully appreciate the functionality of each of the abovelisted entries and the entries use during GSM operation to retrievevalues from within physical memory 430, a description of the process ofassigning a window to support a task of a parallel job is now provided.This process is illustrated by FIG. 6, which is now described.Generally, FIG. 6 is a flow chart of the method of initiating a jobwithin the GSM environment and allocating the various tasks of the jobto specific nodes and assigning a window within the HFI of those nodesto a task, according to one embodiment of the invention.

The process begins at block 602, and proceeds to block 604, at which anapplication generates and issues a GSM initialization operation tolaunch a parallel job. Initialization of the job leads to allocation ofa plurality of tasks to certain nodes across the distributed network, asshown at block 606. At block 608, mapping of these nodes with allocatedtasks is generated and maintained at each node. At each local node withone of these tasks, before using global shared memory, the taskestablishes (or is assigned) a dedicated window on the HFI for thattask, as provided at block 610. A portion of the allocated HFI window(including a command area and FIFO pointers—FIG. 5) is first mapped intothe tasks effective address (EA) space as shown at block 611. Themapping of EA-to-RA for the task is provided to the MMU 121, for lateruse by the HFI during GSM processing. Additionally, the unique job keyor job ID is embedded into the HFI window assigned to the task.

At block 612, the HFI window assignments for the various tasks arelinked to a generated node mapping for the job, and then at block 614,the runtime library communicates task-window identity to other tasks inthe job. This enables each task to be aware of the location of the othertasks and permits subsequent software operations that allocate memory todetermine on which node a certain variable allocated in the globaladdress space should be homed. After the appropriate portion of thetask's effective address space is reserved, the operating system sets upthe HFI window pointer(s) (page table pointer 522) to point to the pagetable for that task so that effective addresses within inbound (i.e.,from the interconnect) GSM commands can be translated at the node, asindicated at block 616. Send and receive pointers (514, 516) are alsoestablished within the HFI window 445 that are translated to specificphysical memory locations by MMU 121.

At decision block 618, the OS determines if the task has multiplethreads. When a task has multiple threads of control, the OS ensuresatomicity to the HFI window through normal intra-task lockingprimitives, as shown by block 620. Alternatively, a task may request aseparate window for each of its threads. At block 622, the window numberwithin the HFI 110 that is allocated during the GSM initializationoperation is returned back to the user space (task) 550 as an opaquehandle, along with the effective address where the global address spaceis reserved within that task's effective address space. Finally, atblock 624, HFI performance counters for all traffic based on that windoware also mapped into the tasks effective address space. This setup ofperformance counters permits the task to easily monitor statistics onthe interconnect traffic. The process then ends at termination block626.

C. GSM Operations

After a global address space is established and memory allocated asgenerally described above (FIG. 6), each task is able to perform thefollowing basic operations: (1) Reads or “gets” to memory; (2) Writes or“puts” to memory; and (3) Restricted atomic operations such as thosebelonging to the set {ADD,AND,OR,XOR,COMPARE_AND_SWAP, FETCH_AND_OP}.Ultimately, all GSM operations are relayed by interconnect messages to(and from) the nodes where a memory location is homed. The basic GSMoperations listed above therefore need to be converted into interconnectmessages that are processed at the appropriate home node. Furthermore,any response messages also need to also be processed at the sending node(i.e., the node receiving a response from a target node for a previouslysent GSM operation). The HFI, and specifically the HFI window allocatedto the particular task, is utilized to provide the hardware support forthese and other GSM-related functions. GSM commands are transmitted by atask to the HFI by simply writing to the memory mapped address space.

The below described embodiments enables different tasks in a (parallel)job to perform operations efficiently on the global address space of theparallel job by using a HFI to issue GSM operations across the fabric ofthe GSM environment. Among the operations that are performed are reads,writes, certain types of atomic operations, and higher level operationsthat can be constructed using one or more of these basic operations.Within GSM task execution, all operations refer to effective addresseswithin the constituent tasks of the GSM job. GSM operations arenon-coherent, can be issued by an application from user-space code, andhave a simple API (application programming interface) that they can beused by the compiler, library, or end-user.

In one embodiment, GSM task execution does not provide/supportload-store access to a location within the global address space that ishomed on a remote node. That is, when a particular global address spacelocation is homed on example target node, a task executing on adifferent node is not able to access the location using a load or storeinstruction. Rather, with GSM task execution, a GSM operation (such as aread, write or atomic operation) must be employed in order to access thelocation. However, the executing task utilizes load and storeinstructions from the PowerPC® ISA (instruction set architecture) toaccess GSM locations that are homed on the node where the task isexecuting.

Turning now to FIGS. 7-9, which provide flow charts illustrating themethods by which the HFI and the HFI window are utilized to enable GSMoperations across different physical nodes of a processing system.Although the methods illustrated in FIGS. 7-9 may be described withreference to components shown in FIGS. 1-5, it should be understood thatthis is merely for convenience and alternative components and/orconfigurations thereof can be employed when implementing the variousmethods. Key portions of the methods may be completed by the taskexecuting within data processing system (DPS) 100 (FIG. 1, 4) andcontrolling access to a GSM location of/on a target node, and themethods are thus described from the perspective of either/both theexecuting task and/or the HFI and HFI window. For example, referring toFIG. 4, a GSM operation is initiated by a task on node A 102 a to alocation that is homed in the effective address space of a task on nodeC 102 b.

GSM commands issued by a task are in the form of operations on locationswithin another task's effective address space. Consequently, theeffective address embedded in a GSM command is meaningless withoutknowing the specific task with reference to which the effective addressmust be translated into a real address. The HFI evaluates received GSMcommands from a local send FIFO before generating the corresponding GSMmessage (packets). HFI and HFI window functionality provides the abilityto launch GSM commands (i.e., interconnect messages) through user-spacecommands.

In the following description, the terms GSM packets, GSM messages, GSMoperations, and GSM data are interchangeably utilized to refer to anycomponent that is transmitted from a first HFI window of an initiatingtask to a network fabric and/or is received from the network fabric at asecond HFI window of a target task. GSM command refers simply to anytask-issued command that is intended to be processed by the HFI andissued to the network fabric. The task also provides non-GSM or standardcommands that are executed on the local processing node.

FIG. 7 illustrates the method by which the HFI generates GSM packetsfrom task-issued commands placed in a send FIFO (first-in first-out)buffer, in accordance with one embodiment of the invention. The processof FIG. 7 begins at block 702, and proceeds to block 704 at which thetask determines a target node in the system to which an EA is homedwithin the GSM. Before a task is able to issue a GSM command, the taskneeds to have or obtain knowledge of the destination node and thedestination node window for directing/addressing the local command. Inone embodiment, the run-time library ascertains the physical node onwhich the task is executing by looking up the mapping table that isgenerated by the POE when the job is first launched. The runtime libraryprovides the task with window information for the selected target node,as shown at block 706. At block 708, the task generates a command withthe destination node and window information included in the command. Itshould be noted that the POE mapping is provide for convenience only.The present invention allows the task identifier to encode thenode/window combination.

Referring to FIG. 4, as part of the command structure, the task on nodeA 102 a creates the GSM command. The command structure includes theidentifier (ID) of the destination/target node and the window on thedestination node against which the message must be examined. Specifyingthe window on the destination node versus specifying the task (executingon the destination node) simplifies the hardware implementation. For putoperations that involve long memory transfers, the task also includesthe start effective address and range information as part of thecommand.

Returning to the flow chart, as provided at block 710, the task writesthe command describing the operation into the send FIFO. These commandsaccumulate in initiating task's cache (FIFO) as the commands arecreated. At block 712, the task's initiator triggers/requests the HFItransmit the stored commands by updating the command countlocation/register, which is physically resident on the HFI window. Aspreviously described, the command count location is memory mapped intothe tasks address space of physical memory. This action constitutes“ringing” the HFI doorbell.

Referring again to FIG. 4, as the task creates GSM commands, the taskkeeps updating the number of operations that need to be handled by theHFI. Commands are created in the send FIFO 407 (FIG. 4), which is backedby local physical memory 408, and can be resident in the cache 405. Thesend FIFO resides in physical memory but is mapped into the task'saddress space and is cacheable by the task. After assembling one or morecommands, the task writes the number of assembled commands to the HFIwindow door bell location 409. In one embodiment, the door bell location409 is physically resident on the HFI 120, but is memory-mapped into thetask's effective address space. The commands at the doorbell location409 are retrieved by the HFI and utilized by the HFI to generate a GSMpacket (containing GSM operations, data or messages) that the HFItransmits to a target task via the network fabric.

In order to transmit a GSM operation, the HFI needs certain bufferresources. As these buffer resources become available, the HFI retrievescommands from the send FIFO. Thus, at decision block 714, HFI logicdetermines if HFI resources are available to transmit the command usingthe task-assigned window. When HFI resources are not currentlyavailable, the task may continue to place new commands (if any) in thesend FIFO, as shown at block 716. However, if there are HFI resourcesavailable, the HFI creates packet headers from the command informationand generates the GSM packets, as shown at block 718. For long putoperations, the HFI also translates the start address and fetches (DMAs)data from the local node. The retrieved data is used to create a GSMmessage. HFI data structures in the window assigned to the task are alsoreferenced/updated. The HFI window tags the job ID of the task to theGSM message, as shown at block 720. The job ID is maintained in the sendwindow and is included as part of every GSM message issued by the HFIwindow. At block 722, the HFI routes the message (as GSM packets)through the interconnect switch. Then, the process of generating the GSMpackets using the HFI ends at termination block 724.

FIG. 8 is a flow chart illustrating the method by which the HFIprocesses a received command from a task executing on the local node,according to one embodiment. The process begins at block 802 andproceeds to block 804 at which the HFI reads/receives the command(s)from the send FIFO when the HFI has the buffering resources necessary totransmit packets on the interconnect. The HFI also receives a count ofthe number of operations that need to be transmitted, so that theprocessor (104, FIG. 1) is decoupled from having to wait while the HFImay be busy transmitting prior commands. Each command either fullydescribes a GSM operation, or contains start and range information forlong “put” (i.e., write data to target) operations. In order tofacilitate GSM operations that operate on small amounts of data, acommand can also contain immediate data, provided the combined commandand data fit within a cache line of, for example, 128 bytes. If a putcommand is larger than some fixed size, the request is put onto the RDMAcommand send FIFO 515. This allows small data movement requests to behandled with higher priority than large data movement requests andprevents large transfers from blocking small transfers.

The HFI identifies the window associated with the task generating thecommands placed in the task's send FIFO, as shown at block 806. The HFIlogic then determines, at block 808, if the command is a legal GSMcommand. A legal GSM command includes the required target node andwindow identifiers, and an operation that is supported via GSMprocessing (e.g., a get, put, or atomic operation), and any otherparameter(s) for generating a GSM packet. When the command is not alegal GSM command, the HFI window discards the command as not supportedby GSM, as provided at block 816, and the HFI window provides anappropriate response/notification to the executing task, at block 818.

However, when the command is legal, the HFI completes a series ofoperations to generate the GSM packets from the command, as indicated atblock 810. Among these operations performed by the HFI are one or moreof (a) creating a packet header from the command information, (b)potentially fetching (via DMAs) data from the local node, and (c)generating the packets. The HFI window then tags the packet with the jobID at block 812, and the HFI window transmits the packets over theinterconnect, at block 814. The process ends at termination block 820.In a system where the individual nodes execute operating systems that donot trust one another, the installed job ID (206) can also be encryptedor hashed to make it tamperproof.

In order to appreciate the generation and issuing of a GSM message(i.e., a GSM operation transmitted via multiple GSM packets) withsequence number and count tuples, an example GSM command andcorresponding example GSM packet are illustrated by FIG. 10. The GSMcommand 1000 includes, without limitation, the following entries, shownwithout regard to actual order: an operation type, which defines whetherthe operation is an atomic operation or a GET or PUT operation, forexample; the source effective address, EA_(S), of the operation, whichis mapped to the memory of the initiating/local task; the targeteffective address, EA_(T), which is mapped to a real address in thelocal memory of the target task; the number of memory locations affectedby the GSM operation; immediate data or the EA of the locally storeddata; and flags indicating whether and/or what type of notification thereceipt/completion of the operation requires. As shown, other entriesmay also be included within the command, and these entries are utilizedto create corresponding entries within the GSM operation generated bythe HFI.

FIG. 10 also illustrates an example GSM packet (of multiple packets)generated by the HFI in response to receiving a GSM command (for amessage that cannot be transmitted by a single GSM packet). As shown, inaddition to the above entries, GSM packet 1020 includes the HFI command(e.g., a remote addition operation), header information, including,without limitation and in no particular order: Job ID, which is theidentification of the globally distributed job (or application), whichID is provided to each GSM packet originating from a tasks of the job;epoch entry, which is set to an actual epoch value for particular typesof operations, when a guaranteed-once notification is assigned as thereliability mode. (A default value indicates a type of operationrequiring a guaranteed-once delivery as the reliability mode; local andremote HFI window and node identifying task and window parameters toidentify to which HFI window (or corresponding task) and at which node aGSMn HFI packet should be directed; and an index for a <sequence, count>n-tuple entry for tracking multiple GSM packets of a single GSMmessage/operation; and a count total of the number of expected packets.

D. Target/Receiving/Destination Node HFI Processing

When the message reaches the destination, hardware support provided byPERCS retrieves the data and sends the response back as a message. Theresponse message is also handled by the HFI of the initiating node,causing the retrieved data to be written to the memory location of theinitiating task. On the receive side of a GSM operation, the job ID inthe packet is compared with the job ID in the target window. If the IDsmatch, the GSM command specified in the message is carried out.

For get operations, the effective address is translated on the targetHFI through the use of MMU 121. Data is fetched from the memory locationof the translated real address, and the data is embedded into a composedmessage and sent back to the initiating task (node). For put operations,the appended data is written to the physical address obtained bytranslating the specified effective address where the data is to bewritten at the target node. In one implementation, GSM atomic operationsare carried out by the memory controller on board the processor chip,such as a Power7™ chip. The processor's internal bus is designed tosupport special transaction types for the atomic operations that areinitiated by the HFI.

FIG. 9 illustrates the method by which the HFI processesreceived/incoming GSM messages (packets) from an initiating node,according to one embodiment. The incoming packets are processed by theHFI using the job ID and EA-to-RA matching table of the target node. Theprocess begins at block 902 and proceeds to block 904 at which the HFIreceives a GSM packet from the interconnect (through the local switchconnection). The HFI parses the GSM packet for the job ID, at block 906.At block 908, HFI examines the job ID included in the message andcompares the job ID with the job ID associated with the various windowssupported/assigned within the HFI. A determination is made at block 910whether the job ID matches one of the supported job IDs. If the job IDof the packet does not match any of the job IDs, the packet isdiscarded, as provided at block 912, and the process ends at terminationblock 920.

In one embodiment, the HFI may also evaluate the window and/or task IDto ensure that the packet has arrived at the correct destination node.As with the job ID, the message is discarded if the window IDinformation does not match that of the target window that is specifiedin the message. Also, in one embodiment, a threshold number of falserequests may be established for each HFI window. When the number ofreceived GSM operations that do not have the correct job ID meets ofsurpasses the pre-established threshold number, an error condition isregistered, which triggers issuance of an administrative notification.

Returning to decision block 910, if the job IDs match, the HFIdetermines, at decision block 911, if a translation exists for the EAwithin the page table pointed to by the page table pointer (522, FIG. 5)within the HFI window. The translation is provided by MMU 121, which isaccessed by the HFI to complete the check for whether the EA-to-RAtranslation is homed on the local node. When no valid translation existsfor the EA received in the message, the local task associated with thewindow is interrupted, as shown at block 913. Several alternatives arepossible. One alternative is to send an error response to the initiatingnode which could then send a non-GSM message to request a validtranslation to be installed. Another alternative is for the interruptedtask to install the required translation, in turn sending an error tothe initiating task if the requested mapping does not exist on thetarget task. When a translation does exist within the page table, theHFI (via the page table) translates the effective address in thereceived message into the corresponding real address, as shown at block914. The translation is performed by referencing the page table that ispointed to within the HFI window. When the address is successfullytranslated, the operation specified by the message is carriedout/performed, as shown at block 916.

The operation is first presented on the internal fabric bus in the chip.The memory controller performs the operation on the memory DIMMs. If thelocations being modified reside on any cache, the cache locations areupdated in place, with the contents being injected into the cache. Atblock 918, the HFI window (via the task) generates and transmits aresponse packet, if such a response is required. The HFI also writesnotifications to the receive FIFO (either writing the notification tomemory or injecting the notification into the cache), as shown at block819. These notifications are visible in the (target) task's effectiveaddress space. The (target) task can also access the locations that weremodified by directly accessing the appropriate location in the (target)task's address space.

The message flows are similar for GSM atomic operations and GSM getoperations. In an atomic operation, the memory controller can performthe atomic operation. Cache injection does not take place for atomicoperations. For a get operation, the HFI does not perform the DMAoperation and instead retrieves (DMAs) data requested by the operation.The retrieved data is assembled into a message that is then sent back tothe initiating node. The HFI on the requester performs the functionsrequired to store the retrieved data into the initiating task'seffective address space.

E. Tracking Completion of Message Delivery Using Sequence-and-CountTuples

A key aspect of the implementation of processing of GSM operations isensuring that the GSM message being issued by the initiating task to thenetwork fabric is completely received by the target task. Often,transmitting a single message from the initiating task to the targettask requires the message be broken up into subparts for transmission.The HFI then transmits the individual subparts of the message viaseparate GSM packets. With this method of transmitting the message insub-parts, reliability of delivery requires some form of trackingmechanism to ensure that all the sub-parts are received by the targettask. In the illustrative one embodiment, the processing of a reliablemessage utilizes sequence number and count tuples.

Also, in some scenarios, the initiating task provides a GSM command thatinvolves a transfer of a large amount of information, requiring multiplenetwork packets to complete the transfer to the target task. When thisscenario arises, the HFI (task) provides a sequence number and counttuple within the GSM packets to track the transfer of the multiple GSMpackets (through different paths in the interconnect) generated by theHFI for the single GSM command.

According to the illustrative embodiment, and as described below, thetasks in the GSM environment utilize a set of sequence number and counttuples (sequence, count) to track delivery of messages that requiredmultiple GSM packets for transmission to a single target task.Specifically, when generating the GSM packets, the HFI logic provides aset of entries within the packet header to enable the target task toidentify the number of packets to be received for the single message aswell as the identity of the packets for that particular message.

Sequence numbers serve two purposes. For atomic operations, which arerequired to fit into one indivisible interconnect flit, the sequencenumber serves to distinguish between whether an atomic operation commandwas dropped or the operation's completion notification was dropped. Fornon-atomic operations, sequence numbers enable an initiating task tohave multiple messages use the same count field. The number of tuplesdetermines the number of outstanding, unacknowledged messages that anoriginating task can have issued to a particular target task.

Every message header of GSM packets generated by the initiating task'sHFI stipulates the number of packets (within the count filed) in themessage. At the target node, the count field keeps track of the numberof packets in the message that have been received so far. The HFI of thetarget node knows that a message has been fully delivered when the countwithin the particular tuple reaches the stipulated number of packets.

E.1 Initiating Task and HFI Tracking of Multi-Packet GSM Messages withPacket Count and Sequence-and-Count Tuples

Once the HFI receives a GSM command (e.g., via a send FIFO or directcache injection), the HFI performs a simple analysis on the received GSMcommand before generating the one or more GSM packets to transmits theinformation required for completing the GSM operation at the targettask. The method by which the GSM packet is generated is illustrated byFIG. 11, which begins at block 1102 and proceeds to block 1104, at whichthe HFI receives a GSM command from an originating/initiating task. Atblock 1106, the HFI logic parses the command to retrieve the relevantinformation related to the operation being requested by the command.Then, at block 1108, the HFI logic evaluates the number of GSM packetsthat would be required to transmit the GSM message/operation. With thenumber of packets determined, the HFI initiates generation of the GSMpacket(s) and inserts the total number of packets in the count totalfield, as shown at block 1110.

The HFI also assigns a sequence number for that series of GSM packets(or a default null value for operations requiring only a single packet),at block 1112. The sequence number is different for each active GSMmessage that the HFI transmits to the same target task, but for whichthe HFI has not yet received a completion notification. With thesequence value assigned, the HFI tags (embeds within) each GSM packet asequence number and count tuple. In one embodiment, the count value issequentially assigned to each packet as a number ranging from 1 throughN, wherein N represents the total number of GSM packets required totransmit the single GSM message. With the count total field and sequencenumber and count tuple assigned to the GSM packet, the HFI issues theset of GSM packets to the network fabric, as shown at block 1113.

The HFI then waits for receipt of a notification of completion from thetarget task, at block 1114. The notification includes the sequencenumber of the set of GSM packets. When, as determined at block 1116, thenotification is received, the HFI places the notification in the receiveFIFO with the notification, and the HFI is thus able to inform the taskof the successful transmission of the particular GSM message. Note thatthe actions in blocks 1114 and 1116 may be completed concurrently forone GSM message with the actions in the previous blocks for another GSMmessage. In other words, while the notification is being checked for afirst GSM message issued to the fabric, the HFI can perform the actionsin the previous blocks to generate and issue GSM packets for a secondGSM message. The task/HFI places the sequence number back into the “tobe assigned” set of sequence numbers, at block 1118. In this way, theHFI may reuse the sequence number from the completed GSM operation (orGSM message delivery) to track transmission of another GSM message tothe target task. The process then ends at block 1120.

E.2 Target Task Handling of Received GSM Packets with Count andSequence-and-Count Tuples

The target task utilizes the count total and sequence number and counttuple within the received GSM packets to assists in guaranteeingcomplete message delivery. The target node's HFI sits on the coherentfabric within the processor chip coupled to the ISR and the networkfabric. With this configuration, the HFI is designed with thefunctionality to support receipt of GSM messages/operations, i.e.,detecting, evaluating and receiving GSM packets and operations from thenetwork fabric.

To determine whether a message has been delivered, the target(receiving) task maintains a set of <sequence,count> tuples at thetarget node in the effective address space of the receiving task. Thetuples are maintained for each other (initiating) task from which thetarget task is receiving a GSM message.

At the target node, the count field keeps track of the number of packetsin the message that have been received so far. Since every messageheader of GSM packets generated by the initiating task's HFI stipulatesthe number of packets (within the count field) in the message, thetarget node's HFI determines that a message has been fully deliveredwhen the count within the particular tuple reaches the stipulated numberof packets. When the target node's HFI receives the full complement ofpackets, the target node's HFI sends a notification message back to theinitiating task. In some embodiments, the target node's HFI alsonotifies the target task, assuming such notification is stipulated inthe message header. After receiving the notification, the initiatingnode is able to reuse the <sequence, count> tuple to transmit a new GSMmessage.

FIG. 12 illustrates the method by which the target node's HFI and targettask provides the guaranteed delivery using the sequence number andcount tuples, according to one embodiment. The process begins at block1202, and proceeds to block 1204 which illustrates the HFIdetecting/receiving a GSM packet (operation) on/from the network fabric.At block 1206, the HFI checks the header information within the GSMpacket for essential identifying parameters, including job ID, epoch,and the like. Target node HFI determines at block 1208 whether theessential parameters check out (are correct when compared topre-established information). When at least one of the essentialparameters does not check out, the HFI rejects the packet, as shown atblock 1209, and the process ends at block 1226.

Assuming, however, the packet contains all essential informationrequired for the HFI to accept/receive the packet, then as provided atblock 1210, the HFI next checks the packet header forinitiating/originating task identifying information, including anindication of the particular GSM message to which the packet belongs.Included in this information is the sequence number assigned to the GSMmessage. The HFI determines at decision block 1212 whether theidentifying information (e.g., sequence number) indicates receipt of anew GSM message.

If the packet is for a new GSM message, the HFI ensures that thesequence number within the message is available and assigns the tuplefor that sequence number to the new massage, as shown at block 1213. TheHFI then proceeds to update the count value (block 1214) in order totrack the number of packets received for that new message.

However, if the received packet is not for a new GSM message, the HFIdoes not need to allocate a tuple because one has already beenpreviously allocated to track receipt of packages for that GSM message.The HFI proceeds directly to block 1214, at which the HFI updates thecount value of the tuple corresponding to the sequence number. At block1215, the HFI then retrieves the count value of the tuple and comparesthe count value against the total number of packets (i.e., the counttotal indicated within the packet header) involved in the transmissionof the GSM message. If, as determined at block 1216, the count valueequals the total number of packets, the HFI then checks for the type ofnotification requested by/for the GSM message, as shown at block 1218.The HFI then generates the requested notification and issues therequested notification to the network fabric, at block 1220. The HFIclears the sequence and count fields of the tuple, to allow use fortracking of a subsequently received GSM message, as shown at block 1222.The HFI also retrieves the operation from the GSM packet and places theoperation within the target task's receive FIFO, as shown at block 1224.The process for guaranteeing reliability of delivery for particularpacket then ends at block 1226.

In one embodiment, the target node's HFI utilizes a structure called ther-context (rCxt) to maintain state about how much of a message has beenhandled. When a packet first arrives, the HFI performs the normal packetverification checks and then the HFI reads the r-context at the offsetdesignated in the header. In the illustrative embodiment of FIG. 4, ther-context is a real memory location within the EAs of the target taskthat are mapped to local memory. The HFI then performs an epoch check,which is described in greater detail in related patent application, Ser.No. ______ (Atty. Doc. No. AUS92007033XUS1). If the epoch is correct,the HFI performs the GSM operation and updates the appropriate sequencenumber in the r-context. In the case of a multi-packet message, the HFIalso increments the count value within the tuple. When the packet headerincludes a notification condition, the HFI generates and issues a replyback to the initiator task, if the condition is satisfied. Finally, ifthe HFI receives a new message, which specifies a different sequencenumber, the count value is zeroed out, and the HFI starts trackingreceipt of the packets for that new message.

In each of the flow charts above, one or more of the methods may beembodied in a computer readable medium containing computer readable codesuch that a series of steps are performed when the computer readablecode is executed on a computing device. In some implementations, certainsteps of the methods are combined, performed simultaneously or in adifferent order, or perhaps omitted, without deviating from the spiritand scope of the invention. Thus, while the method steps are describedand illustrated in a particular sequence, use of a specific sequence ofsteps is not meant to imply any limitations on the invention. Changesmay be made with regards to the sequence of steps without departing fromthe spirit or scope of the present invention. Use of a particularsequence is therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claims.

As will be further appreciated, the processes in embodiments of thepresent invention may be implemented using any combination of software,firmware or hardware. As a preparatory step to practicing the inventionin software, the programming code (whether software or firmware) willtypically be stored in one or more machine readable storage mediums suchas fixed (hard) drives, diskettes, optical disks, magnetic tape,semiconductor memories such as ROMs, PROMs, etc., thereby making anarticle of manufacture in accordance with the invention. The article ofmanufacture containing the programming code is used by either executingthe code directly from the storage device, by copying the code from thestorage device into another storage device such as a hard disk, RAM,etc., or by transmitting the code for remote execution usingtransmission type media such as digital and analog communication links.The methods of the invention may be practiced by combining one or moremachine-readable storage devices containing the code according to thepresent invention with appropriate processing hardware to execute thecode contained therein. An apparatus for practicing the invention couldbe one or more processing devices and storage systems containing orhaving network access to program(s) coded in accordance with theinvention.

Thus, it is important that while an illustrative embodiment of thepresent invention is described in the context of a fully functionalcomputer (server) system with installed (or executed) software, thoseskilled in the art will appreciate that the software aspects of anillustrative embodiment of the present invention are capable of beingdistributed as a program product in a variety of forms, and that anillustrative embodiment of the present invention applies equallyregardless of the particular type of media used to actually carry outthe distribution.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular system,device or component thereof to the teachings of the invention withoutdeparting from the essential scope thereof. Therefore, it is intendedthat the invention not be limited to the particular embodimentsdisclosed for carrying out this invention, but that the invention willinclude all embodiments falling within the scope of the appended claims.Moreover, the use of the terms first, second, etc. do not denote anyorder or importance, but rather the terms first, second, etc. are usedto distinguish one element from another.

1. A method for ensuring complete delivery of a global shared memory(GSM) message from an originating task on a first node coupled to anetwork fabric of a distributed network via a HFI to a target task on asecond node also coupled to the network fabric via a host fabricinterface (HFI), said method comprising: receiving a first GSM packet ofa plurality of GSM packets generated from a single GSM message beingsent from the originating task; assigning a sequence number to trackreceipt of the GSM message from the originating task, said sequencenumber being unique from other sequence numbers assigned to GSM messagesfrom the same originating task that have not been completely received;updating a count value within a tuple comprising the sequence number andthe count value for the first GSM packet and each subsequent GSM packetreceived for the GSM message; and determining when receipt of the GSMmessage is complete by comparing the count value with a count totalretrieved from the packet header, which indicates a total number of GSMpackets being transmitted for the single GSM message.
 2. The method ofclaim 1, further comprising: determining when a notification ofcompletion is to be provided and a type of the notification to provideon receipt of the completed GSM message; generating a notification ofcompletion when the count value is equal to the count total; and issuingthe notification to the network fabric addressed to the originatingtask.
 3. The method of claim 2, further comprising: determining when anotification of completion is to be provided and a type of thenotification to provide to the target task; and placing the notificationof completion in the receive FIFO of the target task when one or moreconditions for notifying the target task are met.
 4. The method of claim1, further comprising: retrieving information related to GSM messagefrom within the first and subsequent GSM packets; and placinginformation retrieved from the first and subsequent GSM packets within areceive FIFO of the target task.
 5. The method of claim 1, furthercomprising: zeroing a count value of a tuple when receipt of the GSMmessage being tracked by the tuple has been completed; and enabling thesequence number and associated tuple to be re-used to track another,subsequent GSM message from the originating task.
 6. The method of claim1, further comprising: receiving, from a local task, a GSM command to beissued to a second task at a remote node across the network fabric;determining a number of GSM packets required to transmit the completeGSM message generated by the GSM command; embedding the number of GSMpackets in each GSM packet as the count total for the GSM message;providing a sequence number within the tuple entry of each GSM packetgenerated for the GSM command; and issuing the GSM packets to thenetwork fabric with the count total and sequence number embeddedtherein.
 7. A processing node within a distributed data processingsystem comprising: a processing unit with a target task executingthereon, said target task being a local task of a distributed job havingmultiple tasks executing at different nodes across a global sharedmemory (GSM) environment; a local memory coupled to the processing unitand having real address (RA) space; a host fabric interface (HFI)including a HFI window assigned to the target task; and programinstructions executing on the processor and providing processing logicfor ensuring complete delivery of a global shared memory (GSM) messagefrom an originating task on a first node coupled to a network fabric ofa distributed network via a HFI to a target task on a second node alsocoupled to the network fabric via a target HFI, wherein the processinglogic instructions comprises processing logic for: receiving a first GSMpacket of a plurality of GSM packets generated from a single GSM messagebeing sent from the originating task; assigning a sequence number totrack receipt of the GSM message from the originating task, saidsequence number being unique from other sequence numbers assigned to GSMmessages from the same originating task that have not been completelyreceived; updating a count value within a tuple comprising the sequencenumber and the count value for the first GSM packet and each subsequentGSM packet received for the GSM message; and determining when receipt ofthe GSM message is complete by comparing the count value with a counttotal retrieved from the packet header, which indicates a total numberof GSM packets being transmitted for the single GSM message.
 8. Theprocessing node of claim 7, said processing logic further comprisinglogic for: determining when a notification of completion is to beprovided and a type of the notification to provide on receipt of thecompleted GSM message; generating a notification of completion when thecount value is equal to the count total; and issuing the notification tothe network fabric addressed to the originating task.
 9. The processingnode of claim 8, said processing logic further comprising logic for:determining when a notification of completion is to be provided and atype of the notification to provide to the target task; and placing thenotification of completion in the receive FIFO of the target task whenone or more conditions for notifying the target task are met.
 10. Theprocessing node claim 7, said processing logic further comprising logicfor: retrieving information related to GSM message from within the firstand subsequent GSM packets; and placing information retrieved from thefirst and subsequent GSM packets within a receive FIFO of the targettask.
 11. The processing node of claim 7, said processing logic furthercomprising logic for: zeroing a count value of a tuple when receipt ofthe GSM message being tracked by the tuple has been completed; andenabling the sequence number and associated tuple to be re-used to trackanother, subsequent GSM message from the originating task.
 12. Theprocessing node of claim 7, said processing logic further comprisinglogic for: receiving, from a local task, a GSM command to be issued to asecond task at a remote node across the network fabric; determining anumber of GSM packets required to transmit the complete GSM messagegenerated by the GSM command; embedding the number of GSM packets ineach GSM packet as the count total for the GSM message; providing asequence number within the tuple entry of each GSM packet generated forthe GSM command; and issuing the GSM packets to the network fabric withthe count total and sequence number embedded therein.
 13. A computerprogram product comprising: a computer storage medium; and program codeon the computer storage medium that when executed on a processing nodeperforms the function of ensuring complete delivery of a global sharedmemory (GSM) message from an originating task on a first node coupled toa network fabric of a distributed network via a host fabric interface(HFI) to a target task on a second node also coupled to the networkfabric via a target HFI, wherein said program code comprising code for:receiving a first GSM packet of a plurality of GSM packets generatedfrom a single GSM message being sent from the originating task;assigning a sequence number to track receipt of the GSM message from theoriginating task, said sequence number being unique from other sequencenumbers assigned to GSM messages from the same originating task thathave not been completely received; updating a count value within a tuplecomprising the sequence number and the count value for the first GSMpacket and each subsequent GSM packet received for the GSM message; anddetermining when receipt of the GSM message is complete by comparing thecount value with a count total retrieved from the packet header, whichindicates a total number of GSM packets being transmitted for the singleGSM message.
 14. The computer program product of claim 13, wherein saidprogram code further comprises program code for: determining when anotification of completion is to be provided and a type of thenotification to provide on receipt of the completed GSM message;generating a notification of completion when the count value is equal tothe count total; and issuing the notification to the network fabricaddressed to the originating task.
 15. The computer program product ofclaim 14, said program code further comprising code for: determiningwhen a notification of completion is to be provided and a type of thenotification to provide to the target task; and placing the notificationof completion in the receive FIFO of the target task when one or moreconditions for notifying the target task are met.
 16. The computerprogram product of claim 13, wherein said program code further comprisescode for: retrieving information related to GSM message from within thefirst and subsequent GSM packets; and placing information retrieved fromthe first and subsequent GSM packets within a receive FIFO of the targettask.
 17. The computer program product of claim 13, said program codefurther comprising code: zeroing a count value of a tuple when receiptof the GSM message being tracked by the tuple has been completed; andenabling the sequence number and associated tuple to be re-used to trackanother, subsequent GSM message from the originating task.
 18. Thecomputer program product of claim 13, said program code furthercomprising code for: receiving, from a local task, a GSM command to beissued to a second task at a remote node across the network fabric;determining a number of GSM packets required to transmit the completeGSM message generated by the GSM command; embedding the number of GSMpackets in each GSM packet as the count total for the GSM message;providing a sequence number within the tuple entry of each GSM packetgenerated for the GSM command; and issuing the GSM packets to thenetwork fabric with the count total and sequence number embeddedtherein.